You planned a route, Maps said one number, and your fitness watch logged something else entirely after the drive or walk was done. Neither is “wrong” – they’re answering different questions. Straight-line distance, road distance, and GPS-tracked distance are three genuinely different measurements, and knowing which one you actually need matters more than assuming one of them is broken. Once you understand the difference, use the CalcRange Distance Calculator for the straight-line figure and Maps for the routed one.
Key Takeaways
- Straight-line distance, road/driving distance, and GPS-tracked distance are three different measurements, not three attempts at the same number.
- Google Maps’ own reported distance can change run to run because its routing engine reacts to current traffic conditions, sometimes suggesting a different route entirely.
- A GPS watch or fitness app can differ from Maps’ prediction due to signal drift, especially in dense urban areas (“urban canyon” effect).
- For planning and budgeting, road distance from Maps is the right figure. For verifying an actual completed trip, a GPS log is more representative.
- None of the three numbers is definitively “correct” independent of what question you’re actually trying to answer.
Three Different Distances, Not One
Straight-line distance (“as the crow flies”) is the shortest possible path between two points, calculated geometrically without regard for roads, terrain, or anything in between – it’s a mathematical lower bound, not a route anyone could actually travel. Road or driving distance is what Google Maps calculates based on the actual road network, following real streets, highways, and turns. GPS-tracked distance is what a phone or fitness watch records by logging your actual position repeatedly during a real trip and summing the distance between those logged points. All three measure something legitimate; they’re just not measuring the same thing.
Why Maps’ Own Number Can Change
Even Maps’ own predicted distance for the “same” route can vary between checks, because its routing algorithm factors in current traffic conditions and may suggest an entirely different physical route – a highway versus back roads, for example – depending on when you check. That’s not a bug; it’s the system optimizing for time or conditions in a way that can genuinely change the actual path length, not just the estimated travel time, between two checks made at different times of day.
Why a GPS Watch Can Disagree With Maps
A GPS device logging an actual completed trip introduces its own sources of variation from Maps’ predicted figure. Positioning error accumulates through small inaccuracies in each logged point, deviations from the planned route (a pedestrian cutting a corner, a driver taking a slightly different turn), and the sampling rate at which points get logged and connected into a total distance, which can either slightly overcount (jittery signal adding phantom back-and-forth movement) or undercount (sparse sampling missing genuine curves in the path) the true distance travelled.
Which Number to Trust for What
For planning a trip or budgeting fuel cost in advance, Maps’ predicted driving distance is the right figure to use, since it reflects the actual road network you’ll travel. For verifying what actually happened on a completed trip – expense reimbursement mileage, exercise tracking, confirming a route was followed – a GPS log is more representative of the real, physical path taken, even with its own small margin of error. Neither one should be expected to exactly match the straight-line distance from our distance-between-two-points guide, which is answering a different, purely geometric question entirely.
Get the Straight-Line Figure
For the geometric, as-the-crow-flies distance between two coordinates, use the CalcRange Distance Calculator. It’s the useful baseline for understanding why road distance is always at least as long, and usually noticeably longer, than the direct line between two points.
The Urban Canyon Effect, Explained
Tall buildings in dense city environments can reflect and block GPS signals, a well-documented phenomenon often called the “urban canyon” effect, which reduces positioning accuracy specifically in downtown areas compared to open terrain. This is part of why a GPS-tracked walk or run through a dense city center can show more measurement noise and inconsistency than the same device would produce in a park or open suburban street, independent of anything about the route itself.
Frequently Asked Questions
Why does Google Maps show a different distance than my GPS watch recorded?
They’re measuring different things – Maps predicts distance along the road network before the trip, while a GPS watch logs your actual tracked position during the trip, introducing its own small positioning errors and any deviation from the planned route.
Why does Google Maps’ distance for the same route change between checks?
Its routing engine factors in current traffic conditions and may suggest a genuinely different physical route depending on when you check, which can change the actual distance, not just the estimated travel time.
Is straight-line distance the same as driving distance?
No – straight-line distance is the shortest geometric path between two points, ignoring roads entirely, while driving distance follows the actual road network and is almost always longer.
Why is GPS tracking less accurate in cities?
Tall buildings can block and reflect GPS signals, a phenomenon known as the urban canyon effect, reducing positioning accuracy compared to open, unobstructed areas.
Which distance should I use to calculate fuel cost for a trip?
Road or driving distance from a mapping service, since it reflects the actual route you’ll travel, unlike straight-line distance which represents a theoretical minimum no road actually follows.
Which distance is more accurate for tracking exercise?
A GPS log from the actual completed activity is generally more representative of what really happened than a pre-trip prediction from a mapping service, even though the GPS log carries its own small margin of error.
The Bottom Line
Straight-line, road, and GPS-tracked distance are three legitimate but different measurements, not three competing attempts at one true number. Use road distance to plan, a GPS log to verify what actually happened, and expect small, explainable gaps between them rather than treating any disagreement as an error.
Last reviewed: August 2026